The posterior pole plasm of the Drosophila embryo acts as a source for a signal that controls the pattern in the posterior region of the embryo. This posterior signal depends on the activity of the maternal gene nanos (nos). The proposed experiments aim towards I) a characterization of the molecular nature of the nos gene product and its distribution during oogenesis and embryogenesis; II) and analysis of the mechanisms by which the nos gene product becomes localized to the posterior pole and III) an understanding of the role of nos in activating zygotic gene expression in the abdominal region. The nos gene will be cloned by chromosomal walking and the coding region sequenced. The distribution of nos RNA and protein in ovaries and early embryos will studied by in situ hybridization to tissue sections and by antibodies. Three different but complementary strategies will be used to associate regions in the nos gene required for its normal localization and stabilization with the specific function of other maternal genes; a) Study of the pattern of nos transcript and protein distribution in maternal mutants known to interfere with nos function. b) Study of the pattern of nos transcript and protein distribution in nos alleles which do not affect transcription. c) Molecular mapping of regions required for localization or stabilization of nos RNA or protein using deletion analysis of P-element mediated transformants. To study the mechanisms by which nos interacts with other maternal gene product as well as the possible role of nos in directing the pattern of zygotic gene expression the native nos protein will be isolated from transformed cell lines.